JP2512643B2 - Method for producing propylene glycol - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing propylene glycol.

[0002]

2. Description of the Related Art 1,2-Dichloropropane (hereinafter referred to as PD
(Abbreviated as C) is produced as a large amount as a by-product when propylene oxide is produced from propylene via chlorohydrin.
In order to effectively use this PDC, PDC was reacted with chlorine at high temperature to induce tetrachloroethylene and carbon tetrachloride. Tetrachlorethylene was in great demand as a raw material for CFC 113, but in recent years, CFC use has been a major issue due to ozone depletion in the stratosphere due to CFC.
It was agreed internationally that it will be abolished by the century. Along with this, tetrachloroethylene which is a synthetic raw material of CFC 113 and PDC which is a raw material of tetrachloroethylene
It is clear that the demand for the PD
There is a need to develop new uses for C.

Already according to GB 1553819, PDC, water, sodium hydrogen carbonate and tributylhexadecylphosphonium bromide at 100 ° C.
Propylene glycol (hereinafter,
A method for obtaining 80% yield of PG) has been proposed. PG is widely industrially used as a polyester raw material and an antifreeze component. Therefore, PDC, which is a by-product,
Converting to G is significant.

[0004]

By the way, according to the above method, the decomposition of sodium hydrogencarbonate produces carbon dioxide gas which is twice the mole of the target PG. Carbon dioxide is thought to cause global warming when released into the atmosphere, and in recent years,
How to prevent the generation of carbon dioxide has become a major issue worldwide. Therefore, when converting PDC into PG in the previous period, it is desirable to collect the carbon dioxide gas generated and not release it into the atmosphere. Also, sodium hydrogen carbonate is relatively expensive, so the method was not economically satisfactory.

It has been desired to develop a method for efficiently and inexpensively obtaining PG from PDC while recovering the carbon dioxide gas thus generated.

[0006]

Therefore, the inventors of the present invention have conducted extensive studies to solve the above problems. As a result, an alkali metal hydrogen carbonate is produced from the alkali metal hydroxide and carbon dioxide, PDC is hydrolyzed using the alkali metal hydrogen carbonate, and carbon dioxide produced as a by-product is formed into an alkali metal hydrogen carbonate. It was found that the above-mentioned problems can be solved by recycle-use in the reaction, and the present invention has been completed.

That is, the present invention comprises a first step of reacting an alkali metal hydroxide with carbon dioxide gas to produce an alkali metal hydrogen carbonate, and an alkali metal hydrogen carbonate obtained in the first step. A second step of reacting 1,2-dichloropropane with each other to produce propylene glycol and carbon dioxide gas, and a third step of circulating the carbon dioxide gas obtained in the second step to the first step Is a method for producing propylene glycol.

The present invention will be described in more detail below. In the present invention, first, in the first step, an alkali metal hydroxide is reacted with carbon dioxide gas to produce an alkali metal hydrogen carbonate. In the present invention, the alkali metal hydroxide is
Known ones are adopted without any limitation. Specific examples thereof include sodium hydroxide and potassium hydroxide, and of these, sodium hydroxide is preferably used.
The alkali metal hydroxide is preferably supplied as an aqueous solution. The concentration of the alkali metal hydroxide in such an aqueous solution may be appropriately determined according to need, but generally a range of 2% by weight to 40% by weight is preferable. The amount of carbon dioxide gas to be circulated and supplied in the first step may be appropriately determined as necessary, but in general, a range of 1 to 5 times the molar equivalent to the alkali metal hydroxide to be supplied is preferable. is there. The reaction temperature in the first step is generally 0 ° C. to 6 ° C. in order to carry out the hydrogenation of the alkali metal hydroxide quickly and stably.
A range of 5 ° C is preferred.

Next, in the second aspect of the present invention, in the second step, the first
PDC using the alkali metal hydrogen carbonate obtained in the process
Is hydrolyzed in an aqueous solution to generate PG and carbon dioxide gas. In the second step, the amount of the alkali metal hydrogen carbonate to be supplied from the first step may be appropriately determined as needed, but in general, the molar ratio is 2 to the amount of PDC.
A range of 10 times equivalent is suitable. In addition, the reaction temperature in the second step is generally preferably in the range of 130 ° C to 300 ° C in order to increase the rate of hydrolysis and prevent a decrease in the yield of the target PG due to side reactions. still,
The partial pressure in the gas phase of carbon dioxide produced as a by-product in the second step is
It is not particularly limited and may be appropriately adjusted as necessary, but generally, it is set to a range of 1 atm to 50 atm from the viewpoint of easy supply of carbon dioxide gas to the third step described later. It is suitable. The method for isolating and purifying the target PG from the reaction solution is not particularly limited, and a known method such as distillation can be employed.

The greatest feature of the present invention is that the carbon dioxide gas generated in the second step by the third step is circulated and supplied to the first step and is used as a raw material for the reaction for producing the alkali metal hydrogen carbonate. is there. In this way, by circulating the carbon dioxide gas generated during the production of PG in the apparatus, the carbon dioxide gas can be effectively used without being released into the atmosphere or the like, and the PG can be efficiently produced.

In the present invention, the reaction system of the first step and the second step is not particularly limited, but a batch system,
Either a semi-batch type or a continuous type may be used, but preferably, FIG.
It is preferable to carry out both steps in a continuous manner as shown in FIG. That is, FIG.
In the figure, 1 denotes a reaction tank for the reaction for obtaining the alkali metal hydrogen carbonate in the first step. And in the reaction tank 1, the pipe 2
Alkali metal hydroxide aqueous solution of more predetermined concentration and piping 3
Further, the carbon dioxide gas by-produced in the second step and circulated in the third step is continuously supplied, and an alkali metal hydrogen carbonate is produced by the hydrogenation reaction. Next, the alkali metal hydrogen carbonate aqueous solution or slurry is continuously supplied to the reaction tank 5 of the reaction for obtaining PG in the second step through the pipe 4. PDC is continuously supplied to the reaction tank 5 through the pipe 6, and as a result, a hydrolysis reaction occurs in the tank to generate PG and carbon dioxide gas. Of these, carbon dioxide gas was extracted from the pipe 3 to the third step while adjusting the pressure in the gas phase, and was again discharged to the first step.
It is circulated and supplied to the process. The PG in the reaction solution is continuously or intermittently extracted from the pipe 7 and then isolated and purified. In the present invention, it is preferable that the first step and the second step react with stirring.

[0012]

INDUSTRIAL APPLICABILITY In the method of the present invention, carbon dioxide gas generated by the production of PG is circulated and used as a raw material for the production of alkali metal hydrogen carbonate, so that the carbon dioxide gas can be effectively utilized without being released into the atmosphere. PG that can be done cheaply and efficiently
Can be manufactured.

[0013]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 PG was produced by the continuous reaction apparatus shown in FIG.
In the first step, a 40 wt% sodium hydroxide aqueous solution was continuously supplied to the reaction tank 1 at a rate of 100 kg / hr through the pipe 2. The reaction temperature of the reaction tank 1 was 30 ° C. Further, in the second step, 144 k of the aqueous solution of 58.3% by weight of sodium hydrogencarbonate produced in the first step was supplied from the pipe 4.
56 kg / hr of PDC from the pipe 6 at the speed of g / hr
Was continuously supplied to the reaction tank 5 at a rate of. The reaction temperature of the reaction tank 5 was 230 ° C. The obtained reaction liquid was continuously extracted from the pipe 7 at a rate of 156 kg / hr. Further, in the third step, the carbon dioxide gas in the gas phase of the reaction tank 5 is extracted through the pipe 3 in a state where the partial pressure of the carbon dioxide gas in the gas phase is 30 atm, and the first step is performed at a rate of 44 kg / hr. Circulated to. As a result of the above, the reaction liquid extracted from the pipe 7 contained 23.1% by weight of PG. The yield of PG was 95% based on PDC.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical embodiment of a method for producing propylene glycol according to the present invention.

[Explanation of symbols]

 1 Alkali metal hydrogen carbonate reaction tank 2 Pipe for supplying alkali metal hydroxide 3 Pipe for circulating carbon dioxide gas 4 Pipe for supplying alkali metal hydrogen carbonate 5 Propylene glycol reaction tank 6 1,2 -Pipe for supplying dichloropropane 7 Pipe for discharging propylene glycol 8 and 9 Pump 10 Stirrer 11 Cooler 12 Valve

Claims (1)

(57) [Claims] 1. A first step of reacting an alkali metal hydroxide with carbon dioxide gas to produce an alkali metal hydrogen carbonate, an alkali metal hydrogen carbonate obtained in the first step, and 1,2-dihydrogen Propylene glycol comprising a second step of reacting chloropropane with each other to produce propylene glycol and carbon dioxide gas, and a third step of circulating the carbon dioxide gas obtained in the second step to the first step. Manufacturing method.